1. Field of the Invention
This invention relates to the field of rotary drive apparatus for rotating substantially cylindrical members such as pipe, tubing, and casing.
2. Description of Prior Art
A number of rotary drive devices wherein the cylindrical member is engaged and driven by a combination of chain and friction drive rollers are disclosed in the prior art. The closest prior art of which the applicant is aware is disclosed in two United States patents: U.S. Pat. No. 3,906,820 granted to Earnest D. Hauk on Sept. 23, 1975 and U.S. Pat. No. 3,892,140 granted to Roy K. N. Fox and Rowan W. Patterson on July 1, 1975. Each of these patents include front rollers with fixed, integral flanges.
The use in prior art apparatuses of rollers with integral fixed flanges results in slippage and in wear. The flange surface of a fixed flange travels at a faster speed than the casing surface. This results in slippage of the flange surface on the casing, since the point of contact between the fixed integral flange and the casing does not coincide with the line of the drive chain pin centers--which line is the only position at which common peripheral speeds exist on the casing and roller assemblies. This slippage causes excessive wear on the fixed flanges requiring their periodic, time-consuming, and expensive replacement.
Another problem with the prior art apparatuses is that, under high torque conditions, the cylindrical member to be rotated "topples," i.e., it lifts away from the front rollers and reacts with the opposite inner edge of the apparatus. This leads to substantial friction losses.